1. Field of the Invention
The present invention relates generally to ink-jet technology, more particularly to characterizing ink-jet performance and, even more specifically, to methods and apparatus for predicting and adjusting ink-jet component performance.
2. Description of the Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. [For convenience, the term xe2x80x9cprinterxe2x80x9d is used hereinafter as generic for all ink-jet hard copy apparatus; no limitation on the scope of the invention is intended by the inventors nor should any be implied.] The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988). As providing background information, the foregoing documents are incorporated herein by reference.
FIG. 1 (PRIOR ART) is a schematic depiction of an ink-jet hard copy apparatus 10. A writing instrument 12 has a printhead 14 having xe2x80x9cdrop generatorsxe2x80x9d for ejecting ink droplets onto an adjacently positioned print medium, e.g., a sheet of paper 16, in the apparatus"" printing zone 34. (The word xe2x80x9cpaper is used hereinafter for convenience as a generic term for all print media; the implementation shown is for convenience in explaining the present invention and no limitation on the scope of the invention is intended by the inventors nor should any be implied.) An endless-loop belt 32 is one type of known manner printing zone 34 input-output paper transport. A motor 33 having a drive shaft 30 is used to drive a gear train 35 coupled to a belt pulley 38 mounted on an fixed axle 39. A biased idler wheel 40 provides appropriate tensioning of the belt 32. The belt rides over a platen 36 in the printing zone 34. The paper sheet 16 is picked from an input supply (not shown) and its leading edge 54 is delivered to a guide 50, 52 where a pinch wheel 42 in contact with the belt 32 takes over and acts to transport the paper sheet 16 through the printing zone 34 (the paper path is represented by arrow 31). Downstream of the printing zone 34, an output roller 44 in contact with the belt 32 receives the leading edge 54 of the paper sheet 16 and continues the paper transport until the trailing edge 55 of the now printed page is released.
It is also known to have an on-board controller 62, electrically connected 60, 64 to the motor, to sensors 41 on the pulley, to the writing instrument 12, and to other electro-mechanical systems of the hard copy apparatus 10. Operation is administrated by the electronic controller 62 which is usually a microprocessor or application specific integrated circuit (xe2x80x9cASICxe2x80x9d) controlled printed circuit board which, if necessary, for the particular hard copy apparatus connected by appropriate cabling to the computer (not shown). It is well known to program and execute imaging, printing, print media handling, control functions, and logic with firmware or software instructions for conventional or general purpose microprocessors or ASIC""s. Within the printing zone 34, graphical images or alphanumeric text are created with the ink droplets deposited on the paper sheet 16 using state of the art color imaging and text rendering via dot matrix manipulation techniques.
A simplistic schematic of a swath-scanning ink-jet pen 12 is shown in FIG. 2 (PRIOR ART). The body of the pen 12 generally contains an ink accumulator and regulator mechanism 200. The internal accumulator and regulator are fluidically coupled 200xe2x80x2 to an off-axis ink reservoir (not shown) in any known manner to the state of the art. The printhead 14 element includes an appropriate electrical connector 201 (such as a tape automated bonding flex tape) for transmitting signals to and from the printhead. Columns of nozzles 203 form an addressable firing array 205. The typical state of the art scanning pen printhead may have two or more columns with more than one-hundred nozzles per column. The nozzle array 205 is usually subdivided into discrete subsets, known as xe2x80x9cprimitives,xe2x80x9d which are dedicated to firing droplets of specific colorants. In a thermal ink-jet pen, the drop generator includes a heater resistor subjacent each nozzle which superheats ink to a cavitation point such that an ink bubble""s expansion and collapse ejects a droplet from the associated nozzle 203. In commercially available products, piezoelectric and wave generating element techniques are also used to fire the ink drops. Other ink-jet writing instruments are known in the art; some, for example, are structured as page-wide arrays. Degradation or complete failure of the drop generator elements cause drop volume variation, trajectory error, or misprints, referred to generically as xe2x80x9cartifacts,xe2x80x9d and thus affect print quality.
In some state of the art ink-jet printers, replacement ink reservoirs are available and thus use the same single writing instrument printhead 14 repeatedly, requiring a longer life than the intended one-time use disposable ink-jet cartridge that contains an on-board ink reservoir. Thus, one of the operational characteristics of concern to the designer is printhead 14 life. One gauge, or xe2x80x9cruler,xe2x80x9d that has been used in the prior art is drop counting. U.S. Pat. No. 5,583,547, DROP COUNT-BASED INK-JET PEN SERVICING METHOD, and U.S. Ser. No. 07/951,255, by Gast et al. describes exemplary methods and apparatus. In the main, drop counting and ink droplet flight-path monitoring provide information useful in controlling printer operations. There are certain advantages for the use of drop counting as a ruler to anticipate some characteristics of the printhead and to adjust future printer activity accordingly. While drop counting is a logical ruler, it has been found that it is not necessarily the best printhead life indicator. Printhead life based on a total drop count for the pen, or even per column count, assumes that the energy to firing nozzles in the array is always the same regardless of firing patterns. In fact, however, the total energy going into the printhead varies from print pattern to print pattern (low frequency text printing energy is substantially less than photo-quality color graphics printing) and from primitive to primitive (i.e., a particular firing sequence may fire from zero to all of the nozzles in a primitive and from one to all the primitives of the entire nozzle array). Thus, drop counting with respect to determining printhead performance and life-expectancy characteristics is effectively only a type of averaging technique.
There is a need for a more accurate predictor of printhead firing element life and performance. The tool should be easily implemented and provide real-time data useful on-the-fly to adjust printer activity or to provide information useful to the end-user.
In a basic aspect, the present invention provides an ink-jet printhead printing method for a printhead having a predetermined matrix of drop generators. The method includes the of: setting a predetermined accumulated energy budget value for each addressable subset of drop generators; determining a next drop generator firing sequence; setting firing energy for addressed subsets of drop generators based on a function of current accumulated energy budget; printing with the next drop generator firing sequence; resetting said predetermined accumulated energy budget value for addressed subsets of drop generators as a function of number of nozzles fired in the step of printing as reset accumulated energy budget values; repeating steps b) through f) for each firing sequence of a current print job; and retaining said reset accumulated energy budget values as said predetermined accumulated energy budget values for a next print job.
In another basic aspect, the present invention provides a method of dynamically adjusting thermal ink-jet printhead drop generator firing energy including the steps of: monitoring energy accumulation values for each separately addressable set of drop generators; and adjusting firing energy to addressed drop generators for a next firing sequence based on the energy accumulation values.
In another basic aspect, the present invention provides a method for scheduling thermal ink-jet printhead servicing, including the steps of: monitoring energy accumulation values for each separately addressable set of drop generators; and performing predetermined printhead service routines based on the energy accumulation values.
In another basic aspect, the present invention provides a computer memory having a tool for measuring thermal ink-jet performance, including: computerized routines for monitoring energy accumulation values for each separately addressable set of drop generators; and computerized routines for indicating printhead performance characteristics based on the energy accumulation values.
In another basic aspect, the present invention provides a method for determining printhead life, including the steps of: monitoring energy accumulation data for a first printhead; comparing data derived from said step of monitoring with predetermined energy accumulation data empirically derived for at least one printhead of a substantially comparable printhead type to said first printhead; and predicting remaining printhead life from data derived from said step of comparing.
In another basic aspect the present invention provides a computer memory for ink-jet printing and servicing including: computer readable routines for setting a predetermined accumulated energy budget value for each addressable subset of drop generators; computer readable routines for determining a next drop generator firing sequence; computer readable routines for setting firing energy for addressed subsets of drop generators based on a function of current accumulated energy budget; computer readable routines for printing with the next drop generator firing sequence; computer readable routines for resetting said predetermined accumulated energy budget value for addressed subsets of drop generators as a function of number of nozzles fired in the step of printing as reset accumulated energy budget values; computer readable routines for repeating the process for each firing sequence of a current print job; and computer readable routines for retaining said reset accumulated energy budget values as said predetermined accumulated energy budget values for a next print job.
Some advantages of the present invention are:
it provides a measurement tool that is based on actual effects incurred by an ink-jet drop generator;
it provides a measurement tool that can be used to alter ink-jet printhead activity and accurately extend printhead life;
it provides a means for lowering ink-jet writing instrument design margins and associated manufacturing costs;
it provides a measurement gauge that takes into account individual nozzle energy use and can adjust firing energy real-time based on prior use;
it provides a method more accurate than state of the art measurement tools in which error factors tend to be cumulative, leading to premature printer activities such as printhead replacement;
it provides a method for predicting and extending printhead life by optimizing drop generator firing element performance and life;
it provides a method for optimizing ink bubble cavitation with minimum wasted energy;
optimized ink bubble cavitation results in lower printhead operation temperatures; and
it provides for better ink drop volume control.
The foregoing summary and list of advantages is not intended by the inventor to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01 (d) merely to apprize the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the FIGURES.